This invention relates to night vision devices and, more particularly, to a high light level cutoff apparatus which can be used to protect a night vision device during high light levels.
As is well known, the term night vision devices include direct view systems employing image intensification. Such systems have various uses but, in general, enable night time vision by responding to low level radiation which is present at night to enable a user to visually perceive a scene or object in the nighttime or in extremely dark environments.
Essentially, night vision devices employ an image intensifier or similar tube. The function of the image intensifier is to multiply the amount of incident light received by it to produce a greater signal for application either to a camera or directly to the eyes of a viewer. As such, these devices have both industrial and military application. An example of early uses of such devices can be had by reference to a text entitled "Photoelectricity And Its Applications" published in 1949 by John Wiley & Sons. Chapter 18 entitled "Light Beam Signaling And Infrared Detection" shows examples of early night vision devices such as the Sniperscope and Snooperscope. Such devices are employed by the military, for example, to enable troops to perceive the enemy at night. In any event, the chapter further discusses various peace time uses.
The development of such devices has followed the strides made in the electronic technologies. The apparatus, as presently employed for night vision, are extremely small and compact. Hence, various companies, such as the assignee herein, produce a number of devices as night vision goggles for enabling one to accomplish night viewing. The assignee herein supplies night vision goggles which are manufactured by IT&T Electro-Optical Products Division of Roanoke, Virginia. These devices enable one to perceive at night with great accuity and perception.
See, for example, U.S. Pat. No. 4,202,601 entitled "Training Aid For Use With Night Vision Apparatus" issued on May 13, 1980 to J. H. Burbo, et al. and assigned to the assignee herein. The patent gives a general description of various night vision devices and other uses and structures.
A most popular device is referred to as night vision goggles. These are portable devices which are powered by small batteries. A night vision goggle is intended to amplify light from a very poorly lit scene so the person needing to see in the dark, as indicated above, can observe the scene clearly using only ambient light, such as starlight, moonlight and so on. These goggles, however, can be inadvertently exposed for long periods of time to bright light while the battery power is still on. This drains the batteries rapidly and also decreases the life of the light amplifying tubes or image intensifier devices.
It is the purpose of a high level cutoff device or switch, which exists in the prior art, to sense the presence of high light levels or light intensity and to switch off the battery power during this condition, thus conserving both the battery and the tube life. It is also noted that there can be flashes of light even in a very dark scene and it is necessary to have the cutoff device operate only when exposed to a high light level for a reasonably long period of time, for example minutes, as compared to seconds. Accordingly, existing devices are equipped with a timer which times out when the high light level is sensed. The existing state of the art incorporates circuitry which serves to provide cutoff for such night vision devices during high light intensities. Such circuits incorporate analog circuitry and are comprised of a combination of specially fabricated integrated circuit chips and standard electronic devices.
In any event, there are specific problems associated with the prior art devices. Such disadvantages will be explained in greater detail in regard to FIG. 1 of the specification.
It is an object of the present invention to provide an accurate, inexpensive and reliable high light level cutoff device which eliminates many of the problems existing in prior art devices as to be described.